(1) Technical Field
The present invention relates to high speed synchronous communication networks and more particularly to a system and a method for creating N-times bandwidth from N separate physical lines.
(2) Description of the Prior Art
The present communication carrier networks have evolved over time from data transmission using mostly analog techniques into entirely digital networks. New industry standards for the transmission and the reception of data have emerged including among other things, methods for channelization, data multiplexing and demultiplexing, switching and cross-connection routing of data from one user to another.
The CCITT Standards specify data signal voltage levels and template characteristics, framing formats, clocking and signal jitter characteristics. The Standards allow the different manufacturers to connect their equipment to the carrier networks and to inter-operate with each other. In the United States, the Standards have been, in particular, the object of a large number of US patents relative to clock recovery, alignment and synchronization within a single channel, as follows:
U.S. Pat. No. 4,394,758, "Timing circuits for PCM reception"--Donne et al. PA1 U.S. Pat. No. 4,394,759, "Digital information transmission system"--Donne et al. PA1 U.S. Pat. No. 4,417,348, "Digital channel protection switching for radio communications"--Abbruscato et al. PA1 U.S. Pat. No. 4,458,356, "Carrier wave restoration circuit for receiver"--Toy et al. PA1 U.S. Pat. No. 4,630,286, "Multiple telephone circuit synchronizer for high speed data"--Betts et al. PA1 U.S. Pat. No. 4,675,886, "Frame synchronizing unit with word-locking decoder"--Surie et al. PA1 U.S. Pat. No. 4,734,920, "High speed modem for multiple communication"--Betts et al. PA1 U.S. Pat. No. 4,744,095, "Diversity channel switch with automatic data rephasing"--Cornet et al. PA1 U.S. Pat. No. 4,775,987, "Transmitter for high bit rate data over telephone system"--Miller et al. PA1 U.S. Pat. No. 4,818,995, "Parallel transmission system using step as line coding type"--Takasaki et al. PA1 1. Application field is limited to the United States telecommunications environment. PA1 2. Delay is not correctly compensated over 5000 meters and limits the transmission distance. PA1 3. No error recovery is provided if one of the lower bandwidth channels becomes inoperative.
Standardization, while useful, is sometimes not cost effective because the granularity of bandwidth to the user does not always meet his needs. The user must reserve bandwidth in the increments tariffed by the individual countries. In Europe and Japan bandwidth is available on E1 and J1 lines, respectively, while in North America bandwidth is available on T1 lines which are the equivalent of E1/J1 lines. See "Newton's Telecon Dictionary" by Harry Newton, Flat Iron Publishing Inc., New York, 8th Edition, published November 1994. If a higher bandwidth is required than provided by a given type of channel, the user is forced to buy the next higher increment of bandwidth even though the tariffed bandwidth far exceeds requirement. For example, in Europe, a user requiring more than the E1 bandwidth of 2 Mbps is forced to buy E3 bandwidth of 34 Mbps. Intermediate rates of bandwidth are not available and the user must buy more bandwidth than required, wasting useful network resources. For purposes of description hereinafter, the term E1/J1 lines shall include T1 lines or equivalent in North America, as indicated in Table 1, supra.
Users in all countries would like to use 2, 3, 4, or more channels, and aggregate them as a single channel rather than pay for a high-speed line with low line utilization most of the time. What prevents the users from doing this directly is that each is individually routed, and may traverse a different geographic path through the network. Thus, the individual control signals experience different transport delay times in passing from the source terminal to the destination terminal. Therefore, the receiving end is not able to reassemble the information in the correct sequence.
Prior art related to the forgoing problem is described in U.S. Pat. No. 5,251,210 entitled "Method and Apparatus for Transforming Low Bandwidth Telecommunications Channels into a High Bandwidth Telecommunication Channel"--Mann et al.--The '210 patent discloses a method for combining lower bandwidth channels to produce a higher bandwidth channel. However, this disclosure is limited in scope because: